Mark has a 100-mile head start (2 hours at 50 miles per hour). Alex is closing at the rate of 70 - 50 = 20 miles per hour. It will take him
... (100 mi)/(20 mi/h) = 5 h
to catch up.
Alex catches up with Mark at 8:00 pm.
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They will meet up 350 miles from uncc.